1. Field of the Invention
The embodiments disclosed herein relate generally to internal combustion engines and more particularly to a high efficiency, high power density and reduced emissions two-stroke engine employing a forced induction system and cylinder scavenging system having multiple valved inlets placed in the cylinder head symmetrically with respect to an axis of the cylinder bore and with unvalved outlets placed in the cylinder wall symmetrically with respect to the axis, the outlets exposed with the piston proximate bottom dead center, and a symmetrically shaped combustion chamber centrally located in the cylinder bore into which at least one fuel injection device introduces fuel symmetrically with respect to the axis.
2. References to Related Art
Internal combustion engines known in the prior art have difficulty providing greater power density, greater efficiency and lower emission levels at once since improvement of one creates penalties in another. More particularly four-stroke engines cyclically operate with one power cycle at every two revolutions of the output shaft, allocating one revolution for the cylinder scavenging process. Two-stroke engines with crankcase ventilation systems cyclically operate with a power cycle at every revolution of the output shaft potentially producing about twice the power compared to four-stroke engines, but producing unacceptable high emission levels due to lack of having a dedicated lubrication system and difficulty controlling the cylinder scavenging process. Two-stroke compression-ignition engines have highly restricted cylinder scavenging systems which results in decreased mechanical efficiency of the engine.
Four-stroke engines with inlet and exhaust valves in the cylinder head may employ four or five valves per cylinder to provide greater volumetric efficiency compared to a more simple two valve system for example. However, the cylinder head has fixed space, which limits the available area for valves. Exhaust as well as inlet valves are required which results in reduced port sizes and associated limitations to volumetric efficiency.
Other disadvantages of four-stroke engines, and particularly Otto cycle engines, are the limitation on the number fuels which can used, as well as limitation of the compression ratios and high heat losses of combustion from high surface-to-volume ratio of the combustion chamber due to the presence of valve reliefs, which result in decreased combustion thermal efficiency. An additional Otto cycle engine disadvantage is high intake pumping losses due to throttling which results in decreased mechanical efficiency.
Other disadvantages of four-stroke engines, and particularly compression-ignition engines, also known as Diesel cycle engines, are high pumping losses in the compression cycle and even more restricted diameters of the valves and ports than Otto cycle engines. Intake of a full charge and high compression in all operating conditions is necessary for Diesel engines to keep the temperature of compressed oxidizer above the self-combustion fuel temperature for ignition.
It is therefore desirable to provide an engine with an efficient less restricted high volume cylinder scavenging system to maximize volumetric efficiency, combustion thermal efficiency and mechanical efficiency with reduced emissions. Additionally, it is desirable to provide an injection-ignition engine with fuel injection directly into the combustion chamber creating ignition from heated fuel injected into the compressed oxidizer, resulting in negligible ignition delay with a greater combustion thermal efficiency. Furthermore, it is desirable to provide an engine accepting high compression ratios with the ability to operate at a variable compression, having reduced pumping losses in both intake and compression cycles and operating with any desired type of fuel. It is also desirable to provide an engine with a two-stroke operation cycle for a greater power density for a particular engine displacement thereby allowing displacement to be reduced for the same engine output requirements. The reduction in displacement results in reduced fuel consumption decreased total emissions, and reduced engine dimensions and weight thereby lowering manufacturing cost.